1. Field of the Invention
The present invention relates to a library apparatus and a hand mechanism included in the library apparatus. More particularly, the present invention is concerned with a library apparatus that has numerous cartridge-type recording media stored in a rack formed in the apparatus, and that records or reproduces data in or from a selected desired recording medium, and a hand mechanism included in an accessor employed in the library apparatus.
2. Description of the Related Art
Along with an increase in an amount of information to be handled in a computer system, a library apparatus adopting a cartridge-type storage medium (hereinafter, simply, a cartridge) that contains magnetic tape has come to be known as an information storage device in which a large amount of information is stored. The library apparatus comprises a plurality of shelves in which numerous cartridges are stored, an access unit that inserts or ejects a cartridge, a drive unit that records or reproduces data in or from a recording medium contained in a cartridge, and an accessor robot (hereinafter, simply, an accessor) that transports a cartridge between the cartridge storage rack and the drive unit.
In recent years, along with sophistication of computer systems, improvement in the reliability of electronic equipment forming a computer system has been required. Moreover, for market competitiveness, the library apparatus must be low cost, be compact, and offer a large storage capacity. It is therefore a must to realize a low-cost, compact, and large-capacity reliable library apparatus and, for example, a large-capacity library apparatus in which several hundreds of cartridges can be stored and about twenty drive units are included.
Moreover, in the large-capacity library apparatus, a hand mechanism that loads or unloads a cartridge in or from a cartridge storage rack plays a pivotal role. A conventional hand mechanism uses a plurality of different motors for different purposes of moving fingers, which hold a cartridge, back and forth (movement for loading or unloading a cartridge), and of causing the finger to hold a cartridge. Thus, the back-and-forth movement and holding movement are controlled mutually independently.
However, since the conventional hand mechanism uses the plurality of motors, the hand mechanism causes a library apparatus to be large in size. Moreover, the increase in the number of motors leads to an increase in a cost and makes it hard to increase the number of cartridges incorporated.
Consequently, a library apparatus having the structure of a hand mechanism thereof made simpler and less expensive has been proposed in Japanese Unexamined Patent Application Publication No. 2003-59143 (FIG. 7 and its description). Herein, the hand mechanism comprises fingers that hold a cartridge, a link mechanism that causes the fingers to hold the cartridge, and a crank mechanism that reciprocates the finger and the link mechanism and drives the link mechanism. The crank mechanism is driven by one motor.
However, although the hand mechanism described in the Japanese Unexamined Patent Application Publication No. 2003-59143 has the features that the structure is simple and compact and the number of motors is small, the hand mechanism suffers a drawback that there is difficulty in adapting the hand mechanism to a large magnetic tape library apparatus. The drawback will be explained in more detail. The size of the library apparatus described in the Japanese Unexamined Patent Application Publication No. 2003-59143 is small, so that the distance moved by an accessor is short. Accordingly, a positional error of the accessor, which increases according to the distance, is small. The apparatus can absorb such a small positional error. However, when the library apparatus is large in size, the distance moved by the accessor increases. Therefore, if the precision in assembling the components of an apparatus or the precision in the dimensions of the components is low, and the accessor is inaccurately positioned in a storage rack in which a cartridge, which the accessor is about to access, is stored.
For example, when the accessor approaches a cartridge storage rack too closely, the fingers included in the hand mechanism fail to advance halfway and fail to reach a normal position. This prevents a crank arm included in the crank mechanism from rotating. Consequently, the link mechanism is not driven, and the fingers attached to the link mechanism cannot hold a cartridge. At worst, the hand mechanism is broken and the cartridge is damaged.